(2) The 7th Infantry Division was to land behind the Marines and advance on their right flank to seize the commanding ground south of Seoul and the south bank of the river (line D-D); to continue the advance to phase line (E-E); and to conduct a reconnaissance in force to the south (line F-F). There, on the line from Suwon to Kyongan-ni, the 7th Infantry Division and 1st Marine Division would form the strategic anvil as Eighth Army forces advanced from the Pusan Perimeter in the role of hammer. (3) The 1st Marine Aircraft Wing was to furnish air support, air direction, and air warning for the Corps with units operating from Kimpo Airfield. It was also to be prepared to operate a control center ashore on order.[91] [91] _Ibid._, v. I, III-B-8, and v. II, app. 16; O. P. Smith, _Notes_, 48–49. The Special Plans Staff gave General Smith a study explaining the purposes of these maneuvers. “The B-B line in this study appeared to be a suitable beachhead line,” he commented, “and we decided to concentrate our efforts on plans for its seizure. Subsequent operations would be reserved for later consideration.”[92] [92] O. P. Smith, _Notes_, 50. _Intelligence Planning for Inchon_ Good planning, of course, depended on accurate intelligence. All possible information about the objective area had been gathered by the staff of PhibGru One before the arrival of the 1st Marine Division planners. Air Force planes had taken hundreds of photographs at every stage of the tide. Hydrographic reports and navigation charts had been studied. Army and Navy men familiar with Inchon during the American occupation after World War II were interrogated as well as NKPA prisoners captured by the Eighth Army. Although a great deal of useful data was compiled, some disturbing questions remained. How high were the sea walls of Inchon? Were the mud flats suitable for landing either troops or vehicles at low tide? Approximately how many NKPA guns were hidden on Wolmi-do?... These were some of the intelligence gaps which must be filled before an effective plan could be drawn up for an assault landing. PhibGru One made its material available to the G-2 Section of the 1st Marine Division, and the two staffs worked together on the _Mount McKinley_ in close cooperation. Attached were the 163d Military Intelligence Service Detachment (MISD) and the 441st Counter Intelligence Corps (CIC) Team. Both of these units had been furnished by FECOM and consisted of Army commissioned and enlisted personnel as well as native Koreans serving in liaison, interpretation, and translation capacities.